One of the therapeutic procedures applicable to the present invention is known as percutaneous transluminal coronary angioplasty (PTCA). This procedure can be used, for example, to reduce arterial build-up of cholesterol fats or atherosclerotic plaque. Typically a guiding catheter is steered through the vascular system to the site of therapy. A guidewire, for example, can then be advanced through the guiding catheter and a balloon catheter may be advanced within the guiding catheter over the guidewire. The balloon at the distal end of the catheter is inflated causing the site of the stenosis to widen. The original catheter can then be withdrawn and a catheter of a different size or another device such as an atherectomy device can be inserted.
The design of medical devices for insertion into body organs has always involved trading off various performance characteristics in the design of a satisfactory implement. PTCA requires a catheter that is stiff enough to be pushable and go through blockage, while being flexible enough to go around bends. Dilatation balloon catheters commonly have a guidewire lumen pass through the balloon with the balloon and guidewire lumen being bonded at the distal end.
Conventional angioplasty balloons fall into high, medium, and low pressure ranges. Low pressure balloons are those that have burst pressures below 6 atmospheres (6.1.times.10.sup.5 Pascals). Medium pressure balloons are those that have burst pressures between 6 and 12 atm (6.1.times.10.sup.5 and 1.2.times.10.sup.6 Pa). High pressure balloons are those that have burst pressures above 12 atm (1.2.times.10.sup.6 Pa). Burst pressure is determined by such factors as wall thickness and tensile strength, for example.
High pressure balloons are desirable because they have the ability to exert more force and crack hard lesions. High pressure balloons are also useful in stent deployment. A biocompatible metal stent props open blocked coronary arteries, keeping them from reclosing after balloon angioplasty. A balloon of appropriate size and pressure is first used to open the lesion. The process is repeated with a stent crimped on a high pressure balloon. The stent is deployed when the balloon is inflated. A high pressure balloon is preferable for stent deployment because the stent must be forced against the artery's interior wall so that it will fully expand thereby precluding the ends of the stent from hanging down into the channel encouraging the formation of thrombus.
High pressure balloon materials are typically stiffer than conventional medium or low pressure balloon materials. Whereas medium or low pressure balloons use materials such as polyethylene, high pressure balloons use materials such as Nylon 12 or polyethylene terephthalate (PET). See, for example, U.S. Pat. No. 4,490,421 (Levy), U.S. Pat. No. Re. 32,983 (Levy), U.S. Pat. No. Re. 33,561 (Levy), and EP 0135990 (Levy), which disclose a high molecular weight, biaxially oriented, flexible, polymeric balloon with a tensile strength of at least 31,714 psi (218.86 MPa), which can be made of PET. See, also, U.S. Pat. No. 5,264,260 (Saab), which discloses a PET balloon, optionally melt blended or mixed with other polymeric or nonpolymeric materials, having an intrinsic viscosity of less than or equal to 0.6 dl/g and a calculated radial tensile strength greater than about 25,000 psi (172 MPa).
Although biaxially oriented PET is advantageous because of its tensile strength, conventional high pressure balloons made only of biaxially oriented PET are very stiff and typically do not have sufficient rewrap such that they can be removed easily after deflation, nor are they sufficiently puncture resistant. Thus, there is a need in the industry for high pressure balloons that have the advantages of biaxially oriented PET, but also display improved rewrap and puncture resistance when compared to balloons made only of PET.